THE CIRCULATION OF THE BLOOD. 163 



the brain became pale and anaemic like other parts. And in death from 

 strangling or drowning, there was congestion of the cerebral vessels; 

 while in death by prussic acid, the quantity of blood in the cavity of the 

 cranium was determined by the position in which the animal was placed 

 after death, the cerebral vessels being congested when the animal was 

 suspended with its head downwards, and comparatively empty when the 

 animal was kept suspended by the ears. Thus, it was concluded, al- 

 though the total volume of the contents of the cranium is probably 

 nearly always the same, yet the quantity of blood in it is liable to varia- 

 tion, its increase or diminution being accompanied by a simultaneous 

 diminution or increase in the quantity of the cerebro-spinal fluid, which, 

 by readily admitting of being removed from one part of the brain and 

 spinal cord to another, and of being rapidly absorbed, and as readily ef- 

 fused, would serve as a kind of supplemental fluid to the other contents 

 of the cranium, to keep it uniformly filled in case of variations in their 

 quantity (Burrows). And there can be no doubt that, although the ar- 

 rangements of the blood-vessels, to which reference has been made, in- 

 sure to the brain an amount of blood which is tolerably uniform, yet, 

 inasmuch as with every beat of the heart and every act of respiration, 

 and under many other circumstances, the quantity of blood in the cavity 

 of the cranium is constantly varying, it is plain that, were there not 

 provision made for the possible displacement of some of the contents of 

 the unyielding bony case in which the brain is contained, there would be 

 often alternations of excessive pressure with insufficient supply of blood. 

 Hence we may consider that the cerebro-spinal fluid in the interior of the 

 skull not only subserves the mechanical functions of fat in other parts as 

 a packing material, but by the readiness with which it can be displaced 

 into the spinal canal, provides the means whereby undue pressure and 

 insufficient supply of blood are equally prevented, 



Chemical Composition of Cerebro-spinal Fluid. The cerebro-spinal 

 fluid is transparent, colorless, not viscid, with a saline taste and alkaline 

 reaction, and is not affected by heat or acids. It contains 981-984 

 parts water, sodium chloride, traces of potassium chloride, of sulphates, 

 carbonates, alkaline and earthy phosphates, minute traces of urea, 

 sugar, sodium lactate, fatty matter, cholesterin, and albumen (Flint). 



(2.) In Erectile Structures. The instances of greatest variation in 

 the quantity of blood contained, at different times, in the same organs, 

 are found in certain structures which, under ordinary circumstances, are 

 soft and flaccid, but, at certain times, receive an unusually large quantity 

 of blood, become distended and swollen by it, and pass into the state 

 which has been termed erection. Such structures are the corpora caver- 

 nosa and corpus spongiosum of the penis in the male, and the clitoris in 

 the female; and, to a less degree, the nipple of the mammary gland in 

 both sexes. The corpus cavernosum penis, which is the best example of 



